When I was about twelve or thirteen, I went to summer school with two young ladies which I will call S and C. We were friends and talked about many sexual things.
On the last night of summer school we were camping outside in seperate tents. The tent that I was in had a leak and it had rained enough that my clothes and sleeping bag were all wet.
We had put the tents right next to each other so that we wouln't have to use as many stakes to hold them down. This would work to our advantage.
Because my clothes were soaked, I had stripped down to the nude and was laying in a dry spot. S called through the sides of the tent to see if I was still awake and if I was naked. When I said that I was, she told me to feel the side of the tent where she was calling from and I would get a suprise.
I felt the tent where she said to and could feel the outline of her breast on the other side. She said that her and C were naked and wanted to have some fun. I asked if they wanted me to come over to their tent and they said that I would cause too much trouble. She said that we should stay where we were but masturbate toghether. We had never done something like this before but I had seen C's bra and she wanted me to use that to jack off to.
After S and C had gotten started, I yanked myself to a good five spurt orgasm and heard C cry out with her orgasm. About two or three minutes later S finished hers.
S and C let me see the panties that they cleaned themselves with later.
This is the only time something like this happened between us. C moved away and S and I grew apart.